1. Field of the Invention
The present invention relates to an apparatus for anchoring prestressed cables.
2. Description of Prior Art
FIGS. 4-6 illustrate apparatus for anchoring prestressed cables such as are presently used in construction. The system comprises a block 1 in which are provided, by any known technique, one or more orifices 2 extending through the block, from one end to the other, through which the prestressed cable 4 passes. The prestressed cables, at one of their ends, in front of the anchorage apparatus are provided with or cooperate with an anchorage system including a block and the cable is extended through the orifice of the block. The major disadvantage associated with anchorage apparatus such as shown in FIGS. 4-6 is the bending of cables 4 at the outlet of the block in curvatures having a very low radius when the axis of the cable (or cables) outside of the block (are) is not perfectly aligned with the axis (or axes) of the bore (or bores) and of the portion of the cable situated on the interior of the block. In such apparatus the cable is guided by the orifice bore through which it extends and at the outlet of the orifice the cable follows the direction which is given to it as a function of the forces exerted on the cable and can be out of alignment with respect to the axis of the guided portion. In such a case, at the outlet of the orifice the cable is supported along a single edge and thus over a very small surface area. Since the prestressed cables are under stress a very substantial force is exerted over a very small surface area which results in a very high pressure on the cable which in turn results in very substantial strains which can cause the rupture of the cable. Likewise, because the curvature has a very low radius (a sharp angle) imposed at the outlet of the anchorage apparatus or block, flexional forces in the cable result which may cause its rupture.
So as to avoid the above disadvantages the bores and orifices of known anchorage blocks are inclined, rather than perpendicular with respect to the exterior surface of the block such that the cables are guided directly in the predetermined direction selected as a function of the forces to be exerted. However, this solution has resulted in other problems. In effect, for each orientation of the cable, the block must comprise one (or more) orifices whose axis of inclination is aligned with the anticipated orientation of the cable. This requires the manufacture of a plurality of blocks having a plurality of orifice orientations provided in the blocks.
Furthermore, the manufacture of these blocks is difficult and thus costly, since the drilling of the orifices must be performed at an angle rather than perpendicular with respect to the exterior surface of commercially available blocks such as is shown in FIGS. 4, 5, and 6.
Another prior art solution proposed to overcome the problems stated above has been to provide the blocks with inclined exterior surfaces such that the blocks themselves are inclined with respect to the surface of the prestressed element on which the block is mounted but along the axis of the cable.
However, this technique results in a number of disadvantages. First, the positioning of the blocks during storage is very difficult by virtue of the ordering necessary with respect to the angles of inclination. Second, this approach is insufficient where one block is used to anchor more than one cable, each cable having different orientations of cables at the outlet of the block. Finally, where the actual inclination is different from that anticipated, all of the problems mentioned above will result.